1. Field of the Invention
The present invention pertains to the art of cooking appliances and, more particularly, to a control element for a cooking appliance that selectively supplies power to a heating element at first and second voltage levels, said power being infinitely adjustable across a temperature selection zone.
2. Discussion of the Prior Art
Infinite temperature controls for controlling heating elements or zones arranged on cooktops of cooking appliances are known. Typically, a element or knob is rotated from an “off” position to a location across a temperature selection zone to establish a desired operating temperature for a heating element. The operating temperature can range from a low setting, typically positioned in a beginning portion of the rotation of the control knob, to a maximum setting, typically positioned adjacent an end portion of the rotation of the control knob. That is, the control knob provides infinite adjustment over an operational finite range so that the control knob actually rotates over a range of less than 360°.
In other arrangements, a control knob can actually rotate more than 360°. The control knob can either be rotated in a first direction to pass over the full temperature range, starting from a low setting and leading to a maximum setting, or the control knob can be rotated in a second direction to pass over the full temperature range, starting at the maximum setting and leading to the low setting. In many cases, the low setting is achieved by activating a single heating element, while the maximum setting is achieved by activating multiple heating elements.
In any event, an infinite switch typically includes a bimetal element coupled to a cycling contact and an internal heater. The internal heater causes the bimetal contact to deform when energy is applied to the internal heater and an internal resistive load. As the load and internal heater are heated, the bimetal contact deforms and the switch opens. When the switch opens, the bimetal contact cools and deforms back to its original, ambient position. At this point, a spring force causes the switch to close and the cycle can be repeated. In general, the infinite switch is employed in a 240 volt AC application and the internal heater is calibrated accordingly.
The cycling of the bimetal contact in a 240 volt system causes the heating element to exhibit significant instantaneous temperature changes. At medium and high temperature settings, these instantaneous temperature changes do not impact food items being heated to any significant degree. However, at lower temperature settings, the instantaneous temperature changes may cause adverse effects to certain food items. For example, melting chocolate and simmering sauces tend to burn even at the lowest temperature settings. To this end, such an infinite switch simply cannot establish the uniform low temperature required to melt or hold delicate food items.
In order to provide a greater degree of control at low temperatures, some manufacturers have proposed to activate the heating element with a lower supply voltage, such as 120 volts AC. The one-half reduction in voltage causes the heating element to operate at one-quarter the power. Operating at lower power enables the heating element to establish the uniform temperature required for cooking and/or holding delicate food items.
In order to achieve the voltage reduction, some manufacturers install a separate switch for toggling between high and low settings, while others provide a dual voltage infinite switch such as indicated at 2 in FIG. 1. Infinite switch 2 includes knob 4 that is rotated across an adjustment region 6 to establish a particular temperature for an associated heating element (not shown). The temperature adjustment region includes a first or low power portion 8 that operates the heating element at 120 volts AC and second or high power portion 10 that operates the heating element at 240 volts. While each of these arrangements provide good low temperature control, each arrangement possesses certain limitations. For instance, in the first example, either a separate toggle switch must be provided for each control or a single toggle can act as a master to all the controls. In the first case, the addition of multiple switches on the cooktop could detract from the overall aesthetics of the appliance, as well as increase the overall complexity of operation. In the second case, a master switch limits the flexibility of the controls. That is, when using a master switch, the consumer must either operate all of the heating elements in a high or low mode. In the second example, the dual voltage switch arrangement addresses this issue by incorporating the toggle switch into the control. While effective at eliminating clutter and the need for additional dedicated switches, the dual voltage infinite switch has a limited adjustment range. That is, only a small portion 8 of the overall adjustment region 6 is dedicated to the low setting.
Based on the above, there exists a need in the art for a control member for a cooking appliance that includes a voltage selector for activating a heating element with either a low voltage setting or a high voltage setting. More specifically, there exists a need for an integrated voltage selector/temperature control that provides a full adjustment zone for each of the low and high voltage settings.